Cationic-anionic surfactant mixtures based on gemini surfactant as a candidate for enhanced oil recovery

The surface and interfacial properties of bisquaternary ammonium salts (16−4−16), sodium dodecyl benzene sulfonate (SDBS), and their mixture were investigated. Moreover, the effects of adsorption on the crude oil/water interfacial tension (IFT) of the SDBS/16–4–16 mixture were examined. Finally, the wettability alternation, oil film peeling-off performance, and core flooding were used to evaluate the enhanced oil recovery of the SDBS/16–4–16 mixture. Results show that the cationic Gemini surfactant 16–4–16 exhibits a strong synergistic effect with SDBS in surface/interfacial activity. At αSDBS = 0.66, the CMC value of the SDBS/16–4–16 mixtures reaches the lowest (0.016 mmol/L), and the interaction parameter (βm) exhibits a minimal value (−11.47), indicating a strong attraction between the cationic and anionic surfactants. When αSDBS is between 0.2 and 0.7, the diesel/water IFT is reduced below 10−2 mN/m, and the IFT shows little relationship with the mixing ratio. For crude oil, when αSDBS is equal to 0.4 and 0.5, the SDBS/16–4–16 mixtures can also reduce the crude oil/water IFT to ultra-low (<10−2 mN/m). When the mineralization is between 5000 mg/L and 20,000 mg/L, the IFT of crude oil/water can be reduced to 3.3 × 10−3 mN/m. Adsorption time, temperature, and liquid-solid ratio have less effect on the IFT of the SDBS/16–4–16 mixture (αSDBS = 0.4) than cationic surfactant 16–4–16. As static adsorption time increases to 24 h, the IFT of the SDBS/16–4–16 mixture only increases from 3.13 × 10−3 mN/m to 4.58 × 10−3 mN/m, while 16–4–16 increases the IFT from 0.121 mN/m to 0.202 mN/m. Furthermore, the SDBS/16–4–16 mixture takes only 10 min to reach dynamic adsorption equilibrium, shorter than the two pure components. The ability of the SDBS/16–4–16 mixtures to reduce the contact angle on the lipophilic glass surface and the oil film peeling-off performance is significantly superior to 16–4–16 and SDBS. As low as 0.1 mmol/L, the SDBS/16–4–16 mixture (αSDBS = 0.4) can reduce the contact angle of oil-wet glass surface from 107° to 46°, while 16–4–16 reduces it to 68° and SDBS to 79°. Eventually, the SDBS/16–4–16 mixture (αSDBS = 0.4) shows excellent performance in the core flooding experiments. The SDBS/16–4–16 mixture could improve crude oil recovery by 26.2%, demonstrating great potential in EOR.